Your hero must be likeable and sympathetic at all times. Like James Bond in the Roger Moore era, he’s quick with a quip, and is unruffled by any situation. No amount of exposure to suffering or slaughter should alter your hero in any significant way, although he is allowed to shed the odd manly tear or to express cold steely determination to do something about the death of a loved one. This makes him even more sympathetic. But all trauma is temporary; showing genuine emotion is difficult, and can hold up the plot. A secret past is always good -- you don’t have to deal with the parents. No bad deed goes unpunished; no good deed goes unrewarded; anyone who disagrees with your hero must suffer for it. Everyone’s behaviour has a rational explanation -- Freud is useful in this respect. No one refuses to get with the plot. Everyone acts their part, and is in character all the time. All problems are solvable. Traditionally, SF heroes solved problems by application of intelligence and scientific knowledge. These days, you can substitute lasers or AK-47s for scientific knowledge. Or swords. The equivalent of the internet or mobile phones are used only when the hero needs to find something out. Usually someone else does the actual typing. Don’t include any science that might frighten the readers. Anything found in SF written before the 1980s is usually okay. Nanotechnology is basically magic. So is genetic engineering. Also quantum mechanics. Virtual reality is more or less the same as a video game. Planets can be treated as a single country, with uniform climate and culture, and no more than three unique features that distinguish them from Earth. Always include some non-Americans for local colour; like the Irish steerage passengers in Titanic
(the movie), they're cheerful, deferential, and possess a quaint and lively culture. Also include either a kickass woman who can do the unacceptable things that would make your hero unlikeable, or a wise old soothsaying woman who speaks in parables and knows things that can’t be found on the internet. See also: sidekick comedy robot. Infodumps can put off readers. Have your characters tell each other about their situation instead. Bars are good places to do this. Bars are also great places to meet people. Unlike airport bars, spaceport bars are packed with colourful characters who all know each other. Aliens can usually be found in the corners of spaceport bars, or in a mysterious rundown quarter of the city attached to the spaceport. They’re basically cats. Or turtles. Or some other pet animal. They often lack a sense of humour, which puts them at a disadvantage when dealing with humans. Interstellar merchants can be found in another corner of the bar, trading in spices, exotic liquors, and rare elements. No matter how technologically advanced your future society might be, its sociology and economics are basically those of the seventeenth century. Also its battle tactics. All spaceships are big. Very big. Except the one owned by the kickass woman. And they never run out of fuel, power, breathable air, potable water, food, or reaction mass. Despite possession of gigantic highly-advanced starships, wars are usually won by your hero and a few good marines. Death is optional. At the end, everything is as it was before, except your hero is richer, more powerful, and married to the right woman, who is never the kickass woman.
There’s your story.